This invention relates to a mesa type semiconductor device, and more particularly to such a semiconductor device having a high breakdown voltage and also having, by itself, means for stabilizing the tilted surface of the mesa portion involved.
In mesa type semiconductor devices of the conventional construction, the mesa portion has been applied with a surface stabilizing film formed of a silicon nitride (Si.sub.3 N.sub.4), phosphosilicone glass, lead oxide (PbO), alumina ( Al.sub.2 O.sub.3) or the like or coated with any of silicone varnishes, silicone rubbers, resins such as polyamides, etc. because the PN junction applied with a reverse bias has its circumference exposed to the surface of the mesa portion and therefore a leakage current must be prevented from flowing across the exposed portion of the PN junction.
The surface stabilizing film is advantageous in that it can be attached to one of the main opposing surfaces of semiconductor wafers before the wafers are divided into individual chips. However, upon forming windows on selected portions of the surface stabilizing film in a later step according to the selective etching technique, those portions of the film located at the edges of the mesa portions are decreased in thickness. As a result, the surface stabilization is not satisfactorily accomplished. This is because the mask or the photoresist used upon the formation of the windows as described above is not satisfactorily applied to those portions of the surface stabilizing film at and adjacent to the edges of the abovementioned mesa.
With the varnishes or resins used, the electric characteristics of the semiconductor elements are confirmed only after the associated semiconductor chips have been subjected to die bonding and still the sintering of the resins consumes a long time. This has resulted in a decrease in work efficiency.
Accordingly, it is an object of the present invention to provide a new and improved mesa type semiconductor device able to withstand high breakdown voltages.
It is another object of the present invention to provide a new and improved mesa type semiconductor device having a reduced surface leakage current and including a much stabilized surface of the mesa portion.
It is still another object of the present invention to provide a new and improved mesa type semiconductor device manufactured with excellent work productivity.